MSE + h264 in Opera 29 not working on Youtube

I've been looking forward to Opera adding support for this, but now that it's here I can't get it to work. When I enable the feature, Youtube just gives me the generic "An error has occurred. Please try again later." When I turn MSE + h264 support off, Youtube works again but I can't view videos in 1080p. Youtube's html5 test page shows all features available when the option is on.

I have verified that playback of proprietary media types is enabled and I have an h264 codec installed. Am I missing something?

It says in the title Opera 29. I was reading reports of people using the Opera 29 beta a couple weeks ago with this feature enabled and no problems on Youtube, but it's possible they were only looking at the html5 feature test page. I suppose I can wait another month if the feature isn't finished yet.